The field of the invention is the production of alkyl esters of saturated aliphatic carboxylic acids and the present invention is particularly concerned with reacting olefins with carbon monoxide and alkanol in the presence of a catalyst consisting of a cobalt compound and a promoter selected from pyridine, non-ortho-substituted alkylpyridine or mixtures thereof at elevated pressures and elevated temperatures and with feedback of unconverted input materials.
The state of the art of such alkoxycarbonylation reactions may be ascertained by reference to U.S. Pat. Nos. 3,507,891; 3,906,016; and 4,041,057, and the article, "Hydrocarboxymethylation--an Attractive Route from Olefins to Fatty Acid Esters?" by Peter Hofmann et al as published in I & EC, Product Research and Development, Vol. 19, Sept. 1980, pp. 330-334, the disclosures of which are incorporated herein.
It is known to prepare fatty acid esters by reacting olefins with carbon monoxide and a compound having a replaceable hydrogen atom such as an alkanol in the presence of a catalyst containing a metal of Group VIII of the Periodic Table of elements and possibly also a promoter as disclosed by J. Falbe, "Synthesen mit Kohlenmonoxid", Springer publisher, Berlin, Heidelberg, New York (1967).
An especially preferred variation of this reaction, which is termed alkoxycarbonylation, has been found to be the conversion in the presence of a cobalt catalyst. An especially preferred embodiment consists in further adding a promoter, especially pyridine, non-ortho-substituted alkylpyridines and mixtures thereof.
The economy of such a process for making fatty acid esters depends decisively on the ester yield to be achieved. This yield, in the case of, for instance, a procedure for feeding back unconverted input and accessory materials into the alkoxycarbonylation stage as disclosed in U.S. Pat. No. 4,041,057 is degraded by the formation of those by-products which have a higher boiling point than the desired reaction products, these by-products being termed high boiling substances. On account of the formation of these high boiling point substances, there results not only a higher olefin consumption per unit weight of the desired end product, but also losses of other valuable input materials in the course of the necessary separation of these high boiling point substances.